1,720,959 research outputs found
Surface Discharge Measurements of Polymeric Materials
No full textThe measurement of surface charge is an important parameter for evaluating the electrical performance of high voltage insulation materials. The method proposed allows on line measurement of charge and can generate two-dimensional images that represent the charge behaviour on the surface of the material under test. The measurement system utilises Pockels effect by using a wafer of bismuth silicon oxide (BSO) as the sensing element. This method allows non-destructive measurements since no direct electric signal or component interferes with the surface charge. Unlike conventional surface charge measurement systems, this approach can dynamically observe and simultaneously quantify surface charge. This allows the surface charge distribution under the influence of a time varying electrical field to be studied. the system's accuracy and sensitivity have been improved through the use of an optical phase modulator. The system uses a high speed CCD camera and a purpose built synchronisation control circuit to obtain a high temporal resolution. This has allowed the study of charge behaviour at mains frequencies. Surface charge distributions have been observed by applying AC voltages to a needle electrode in direct contact with the BSO. AC surface discharge behaviour of polymeric materials bonded to the back-face of the BSO has also been investigated
Dynamic AC surface discharge characteristics of PMMA and LDPE
No full textPolymeric materials such as Low Density Polyethylene (LDPE) and Polymethylmethacrylate (PMMA) have properties that are ideal for use as electrical insulating materials within a wide range of commercial products. They have good mechanical properties and the advantages of high electrical breakdown strength, high electrical resistivity and low dielectric loss. In many practical applications involving the use of insulation, high electrical stresses can be generated at the edges of the interface between a conductor and the solid insulation by the existence of a non-uniform electric field. This may cause local sparking and or corona along the surface of the insulation. The presence of surface discharge activity is a significant problem for polymeric insulators. Any discharge can cause a slow deterioration of the insulator surface in the long term through three mechanisms: firstly through slow erosion by ionic bombardment of ions in the sparks, secondly by chemical degradation of the insulation material and thirdly from carbonisation of the material surface. Conducting deposits are formed on the surface and this will influence the electrical characteristics of the insulator. The development of a suitable method to monitor surface discharge behaviour of high voltage insulating materials is therefore of particular interest
The influence of local environmental conditions on surface discharge behaviour
No full textThe measurement of surface charge is important in determining the electrical performance of high voltage insulation materials. This paper is concerned with surface charge measurements utilising Pockels effect. The method proposed allows on-line measurement of charge and can generate two-dimensional images that represent the charge behaviour on a material surface. The system has been used to investigate the influence of local environment on surface charge distribution
Dynamic measurement of surface charge
No full textThis paper describes the development of a system capable of monitoring the dynamic movement of surface charge on insulating materials. High electrical stress can be generated at the edges of an interface between a conductor and solid insulation by the existence of a non-uniform field. This may cause local sparking and corona along the surface of the insulation. The presence of surface discharge activity is a significant problem for organic insulators. Any discharge can cause a slow deterioration of the insulator surface in the long term through three mechanisms: Slow erosion by ionic bombardment of ions in the sparks, chemical degradation and carbonisation of the surface material. Conducting deposits are formed on the surface and this will influence the electrical characteristics of the insulator. The development of a suitable method to monitor surface discharge behaviour of high voltage (hv) insulating materials is therefore of particular interest
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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